Helical dislocations as vacancy sinks in β phase Cu–Zn–Al–Ni alloys

The microstructure of a quenched β phase Cu–Zn–Al–Ni alloy has been analysed by transmission electron microscopy. Different types of dislocations were observed, which seemed to be the main vacancy sinks. They are present as single dislocations, loops and helical dislocations. The latter had axes perpendicular to the Burgers vector, spreading around an angle of 30° from the nearest 〈1 0 0〉 direction. No γ precipitates were observed in this Ni-containing alloy, in sharp contrast to that in Cu–Zn–Al of similar electron concentration. The reason for this difference is examined, and the consequences of the presence of Ni on the ageing behaviour of the alloy are discussed.